Rotary pump with electromagnetic LCR bearing

ABSTRACT

A pump ( 10 ) includes a housing ( 14 ) having a fluid inlet ( 26 ) and a fluid outlet ( 28 ). A rotor ( 12 ) is disposed within the housing ( 14 ) and rotatable about an axis ( 16 ) to move fluid from the fluid inlet ( 26 ) to the fluid outlet ( 28 ). A magnetic axial bearing ( 286 ) for supporting the rotor ( 12 ) includes an axial bearing target ( 70 ) disposed on the rotor and an axial bearing stator ( 130 ) disposed on the housing, the axial bearing stator including multiple stator poles ( 132   a,    132   b,    132   c ) each including a first coil portion wound in a first direction and a second coil portion wound in a second direction opposite the first direction.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/508,618, which was filed on Oct. 2, 2003 and is incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to a rotary pump with an electromagneticLCR bearing for supporting the pump rotor.

BACKGROUND OF THE INVENTION

Heart disease is the leading cause of death and disability in the UnitedStates. Some approaches to the treatment of heart disease employ the useof pumping systems that are used to assist the heart in its pumpingfunction, bypass the heart, or replace the heart. Such pumping systemsmay include pumps that are implantable or pumps that remain external tothe patient. One example of a pumping system is a post-cardiotomy assistsystem. Another example of a pumping system is a bridge-to-transplantsystem for assisting or replacing a patient's heart while awaiting atransplant. A further example of a pumping system is abridge-to-recovery system, such as a ventricular assist device (VAD),that assists the patient's heart in order to promote myocardialrecovery, either spontaneously, with drugs, or with gene therapy.

SUMMARY OF THE INVENTION

The present invention relates to a pump including a housing having afluid inlet and a fluid outlet. A rotor is disposed within the housingand is rotatable about an axis to move fluid from the fluid inlet to thefluid outlet. A magnetic axial bearing supports the rotor. The axialbearing includes an axial bearing target disposed on the rotor and anaxial bearing stator disposed on the housing. The axial bearing statorincludes multiple stator poles, each of the stator poles including afirst coil portion wound in a first direction and a second coil portionwound in a second direction opposite the first direction.

The present invention also relates to a pump including a housing havinga fluid inlet and a fluid outlet. A rotor is disposed within the housingand is rotatable about an axis to move fluid from the fluid inlet to thefluid outlet. A magnetic first radial bearing exerts a force on therotor in a first direction along the axis and a magnetic second radialbearing exerts a force on the rotor in a second direction along the axisopposite the first direction. The first and second radial bearings areadjustable to allow for independently adjusting the net axial forceexerted on the rotor by the radial bearings and the radial stiffness ofthe radial bearings.

The present invention also relates to a pump including a housing havinga fluid inlet and a fluid outlet. A rotor is disposed within the housingand is rotatable about an axis to move fluid from the inlet to theoutlet. The rotor includes permanent magnets arranged on a first side ofthe rotor and a magnetically conductive disk arranged on a second sideof the rotor opposite the first side of the rotor. A motor stator isarranged on the housing to interact with the permanent magnets on therotor. At least one electromagnet is arranged on the housing to interactwith the magnetically conductive disk on the rotor. At least one ringmagnet is arranged on at least one of the first and second sides of therotor. At least one ring magnet is arranged on the housing tomagnetically interact with the at least one ring magnet on the rotor.

The present invention also relates to a pump including a housing havinga fluid inlet and a fluid outlet. A rotor is disposed within the housingand is rotatable about an axis to move fluid from the inlet to theoutlet. A motor is arranged to cause rotation of the rotor. At least oneelectromagnet is arranged to interact magnetically with material in therotor. The electromagnet includes a stator formed from a spiral woundlamination material.

The present invention also relates to a pump including a housing havinga fluid inlet and a fluid outlet. A rotor is disposed within the housingand is rotatable about an axis to move fluid from the inlet to theoutlet. A motor is arranged to cause rotation of the rotor. At least oneelectromagnet is arranged to interact magnetically with material in therotor. The electromagnet includes an even number of poles, adjacentpoles being wound in opposite directions.

The present invention also relates to a pump including a housing havinga fluid inlet and a fluid outlet. A rotor is disposed within the housingand is rotatable about an axis to move fluid from the inlet to theoutlet. A motor is arranged to cause rotation of the rotor. At least oneelectromagnet is arranged to interact magnetically with material in therotor. The material includes a disk of spiral wound magnetic alloymaterial.

The present invention also relates to a method for magneticallysupporting a pump rotor in a housing for rotation about an axis. Themethod includes the step of providing an axial bearing target on therotor. The method also includes the step of providing an axial bearingstator on the housing, the axial bearing stator including multiplestator poles, each including a first coil portion and a second coilportion. The method also includes the steps of winding the first coilportion in a first direction and winding the second coil portion in asecond direction opposite the first direction.

The present invention further relates to a method for magneticallysupporting a pump rotor in a housing for rotation about an axis. Themethod includes the step of providing a magnetic first radial bearingfor exerting a force on the rotor in a first direction along the axis.The method also includes the step of providing a magnetic second radialbearing for exerting a force on the rotor in a second direction alongthe axis opposite the first direction. The method further includes thestep of adjusting the axial positions of the first and second radialbearings to independently adjust the net axial force exerted on therotor by the radial bearings and the radial stiffness of the radialbearings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates upon reading the following description with reference to theaccompanying drawings, in which:

FIG. 1 is a perspective view of a pump apparatus according to thepresent invention;

FIG. 2 is an exploded view of the apparatus of FIG. 1;

FIGS. 3A and 3B are side views illustrating a portion of the apparatusof FIGS. 1 and 2;

FIGS. 4A and 4B are side views illustrating alternative configurationsof a portion of the apparatus of FIGS. 1 and 2;

FIGS. 5A-5C are schematic illustrations depicting the operation of aportion of the apparatus of FIGS. 1 and 2;

FIG. 6A is a schematic illustration depicting the operation of a portionof the apparatus of FIGS. 1 and 2; and

FIG. 6B is a graph illustrating certain operating parameters of theapparatus of FIGS. 1 and 2.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a rotary pump that includes magneticbearings for supporting the pump rotor by magnetically levitating therotor. In one embodiment, the pump may comprise a blood pump forincorporation in a system for pumping blood in a patient. For example,the pump may be a cardiac assist pump or a cardiac replacement pump. Thepresent invention, however, is not necessarily limited to blood pumpsand could have alternative implementations or uses in which the pump isused to pump alternative fluids.

FIGS. 1 and 2 illustrate an example configuration of an apparatus in theform of a pump 10 for pumping fluids. The pump 10 may, for example, be ablood pump. In the embodiment of the invention illustrated in FIGS. 1and 2, the pump 10 is a rotary pump in which a rotor assembly or rotor12 is supported in a housing 14 for rotation about an axis 16. Thehousing 14 includes a central volute housing part 20, a motor statorhousing part 22, and an inherently controlled bearing (ICB) statorhousing part 24. The motor stator housing 22 and ICB housing 24 areconnectable to the volute housing 20 on opposite sides of the volutehousing, thus forming the assembled condition of the housing 14 shown inFIG. 1. The pump 10 includes an inlet 26, associated with the motorstator housing 22, through which fluid is directed into the pump. Thepump 10 also includes an outlet 28, associated with the volute housing20, through which fluid is discharged from the pump.

Referring to FIGS. 2, 3A, and 3B, the rotor 12 includes an impellerstructure 30 that includes a generally disk shaped motor side end wall32 and a generally disk shaped ICB side end wall 34. The end walls 32and 34 are spaced from each other, parallel to each other, and centeredon the axis 16. The impeller structure 30 also includes a plurality ofimpeller vanes 36 that extend between the end walls 32 and 34 and helpdefine a plurality of impeller passages 38. A central axially extendinginlet passage 40 extends through the rotor 12 is in fluid communicationwith the impeller passages 38.

Referring to FIGS. 2 and 3A, the motor side end wall 32 supports a motorpermanent magnet (PM) ring 50 and a motor side PM radial bearing ring 60of the rotor 12. The motor side PM radial bearing ring 60 is positionedradially inward of the motor PM ring 50. An annular insulating portion52 may help isolate the motor PM ring 50 and the motor side PM radialbearing ring 60. The motor PM ring 50 and motor side PM radial bearingring 60 are fixed to or embedded in the motor side end wall 32 of therotor 12. The motor PM ring 50 includes a plurality of PM motor magnets54 arranged in an annular fashion about the motor side end wall 32. Inthe embodiment illustrated in FIG. 2, the motor PM ring 50 includeseight (8) motor magnets 54 equal in size and arranged spaced evenly inan annular fashion about the motor PM ring 50. The motor PM ring 50could, however, have an alternative configuration, such as including adifferent number of PM motor magnets 54.

The motor side PM radial bearing ring 60 may be made of a permanentmagnet material with high coercivity such as neodymium boron iron. Themotor side PM radial bearing ring 60 has an annular single magnetconstruction. The motor side PM radial bearing ring 60 could, however,have an alternative construction. For example, the motor side PM radialbearing ring 60 may include multiple magnet segments and may includeflux carrying material, such as iron, to aid in creating a desiredmagnetic flux path.

Referring to FIGS. 2 and 3B, the bearing side end wall 34 supports aring-shaped axial bearing target 70 and a bearing side PM radial bearingring 80 of the rotor 12. The bearing side PM radial bearing ring 80 ispositioned radially inward of the axial bearing target 70. An annularinsulating portion 72 of the bearing side end wall 34 may help isolatethe axial bearing target 70 and the bearing side PM radial bearing ring80. The axial bearing target 70 and bearing side PM radial bearing ring80 are fixed to or embedded in the bearing side end wall 34 of the rotor12. The axial bearing target 70 has an annular configuration and isconstructed of ferrite, powder iron, or laminated silicon steel. Forexample, the axial bearing target 70 could be formed from a thin flatstrip or strips of material that are wound to form the axial bearingtarget. The axial bearing target 70 could, however, have an alternativeconfiguration, an alternative material construction, or both.

The bearing side PM radial bearing ring 80 may be made of a permanentmagnet material with high coercivity such as neodymium boron iron. Thebearing side PM radial bearing ring 80 has an annular single magnetconstruction. The bearing side PM radial bearing ring 80 could, however,have an alternative construction. For example, the bearing side PMradial bearing ring 80 may include multiple magnet segments and mayinclude flux carrying material, such as iron, to aid in creating adesired magnetic flux path.

The volute housing part 20 (FIG. 2) has a generally cylindrical mainportion 100 that helps define a volute pump chamber 102. The mainportion 100 has a first end forming a motor side 106 of the volutehousing 20 and an opposite second end forming a stator side 108 of thevolute housing. The pump chamber 102 is sized to receive the rotor 12and form a predetermined clearance with the rotor. An annular pumpingchannel 104 is formed in the main portion 100 an is in fluidcommunication with the pump chamber 102 and the impeller passages 38when the pump 10 is assembled. The outlet 28 extends generallytangentially from the main portion 100 of the volute housing part 20 andis in fluid communication with the pumping channel 104.

The motor stator housing 22 is adapted to support a motor statorassembly 120 of the pump 10. In the illustrated embodiment, the motorstator assembly 120 includes six (6) motor stator coils 122 arranged inan annular configuration. Each motor stator coil 122 is made of copperwire that is wound in layers around posts 128 formed on a core 124. Thecore 124 may be formed of a ferromagnetic material, such as a powderediron material or a silicon steel material, and thereby serve as a fluxreturn path. This may help improve the torque per unit coil currentratio of the pump 10. Alternative materials could be used to form themotor stator coils 122, the core 124, or both.

The motor stator assembly 120 is connected to the motor stator housing22 by means (not shown) such as an adhesive. Alternative means may beused to secure the motor stator assembly 120 to the motor stator housing22. The motor stator assembly 120, particularly the motor stator coils122, may also be sealed or covered with a material, such as a film, thatis coextensive with an annular inner surface 126 of the motor statorhousing 22. The assemblage of the motor stator housing 22 and motorstator assembly 120 may thus have a generally flat smooth surfaceexposed to the pump chamber 102.

The bearing stator housing 24 is adapted to support an ICB bearingstator assembly 130 of the pump 10. Alternative embodiments for thebearing stator assembly 130 are illustrated in FIGS. 4A and 4B,respectively. In the embodiment illustrated in FIGS. 2 and 4A, thebearing stator assembly 130 includes six (6) bearing stator coils 132arranged in an annular configuration. In the embodiment illustrated inFIG. 4B, the bearing stator assembly 130 includes three (3) bearingstator coils 132 arranged in an annular configuration. In theembodiments of FIGS. 4A and 4B, each bearing stator coil 132 is made ofcopper wire that is wound in layers around stator posts 136 on an axialbearing stator core 134. The axial bearing stator core 134 may beconstructed of a ferromagnetic material and thus may serve as a fluxreturn path. Alternative materials could be used to form the bearingstator coils 132, the axial bearing stator core 134, or both.

Referring to FIG. 2, the bearing stator assembly 130 is connected to thebearing stator housing 24 by means (not shown) such as an adhesive.Alternative means may be used to secure the bearing stator assembly 130to the bearing stator housing 24. The bearing stator assembly 130,particularly the bearing stator coils 132, may also be sealed or coveredwith a material, such as a film, that is coextensive with an annularinner surface 138 of the bearing stator housing 24. The assemblage ofthe bearing stator housing 24 and bearing stator assembly 130 may thushave a generally flat smooth surface exposed to the pump chamber 102.

Referring to FIG. 4A, the six bearing stator coils 132 of the bearingstator assembly 130 are configured for three phase excitation. In thisconfiguration, adjacent pairs of the bearing stator coils 132 are woundwith the same wire and excited with the same voltage phase. In thisconfiguration, three pairs of bearing stator coils form three bearingcoil poles 132 a, 132 b, and 132 c. Each bearing stator pole 132 a-c canbe excited with a different phase of the three phase voltage. In thisconfiguration, the individual bearing stator coils 132 of the bearingpoles 132 a-c may be wound in opposite directions. For example, for eachpole 132 a-c, one coil 132 may be wound in a clockwise direction and theother coil may be wound in a counterclockwise direction. This isindicated generally by the arrows in FIG. 4A.

In the embodiment illustrated in FIG. 4B, the three bearing stator coils132 of the bearing stator assembly 130 form three bearing stator poles132 a, 132 b, and 132 c. Referring to FIG. 4B, the three bearing statorpoles 132 a-c of the bearing stator assembly 130 are configured forthree phase excitation. Each bearing stator pole 132 a-c can be excitedwith a different phase of the three phase voltage.

Referring to FIG. 2. the pump 10 also includes a motor seal assembly 200that includes a generally disk shaped motor side seal 202 and a tubularport 204 that projects centrally from the motor side seal. The port 204defines the inlet 26 of the pump 10. The motor side seal 202 includes anannular bead 210 that is adapted to be received in an annular shoulderor recess 212 in a motor side surface 214 of the volute housing part 20.A generally planar membrane portion 216 extends radially inward from theannular recess 212. As an example, the motor side seal 202, particularlythe membrane portion 216, may be constructed of a sheet of polycarbonateconnected to the bead 210 by an adhesive. The motor side seal 202 mayhave a mechanical stiffness derived from radial tensioning of the seal,back support from the motor stator 120, or both.

The port 204 projects perpendicularly from the membrane portion 216 andextends along the axis 16. The port 204 may be connected to the membraneportion 216 by an adhesive. The port 204 could project from the membraneat some other angle or could have an extent other than along the axis16, such as a curved extent. As shown in FIG. 2, an annular projection208 may project opposite the port 204. The projection 208 may helpdirect fluid flow into the inlet passage 40 of the rotor 12. Theprojection 208 may also serve as a small diameter or small surface areastop point for excessive axial travel of the rotor 12.

The pump 10 also includes a bearing seal assembly 220 that includes agenerally disk shaped bearing side seal 222 and an O-ring 224. Thebearing side seal 222 includes an annular groove 226 for receiving theO-ring 224. The volute housing part 20 may include a similarly oridentically configured annular groove (not shown) for receiving theO-ring 224 that is recessed into a bearing side surface 232 of thevolute housing part. The bearing side seal 222 also includes an annularbead 234 that is adapted to be received in an annular shoulder or recess236 of the bearing stator housing 24. The bearing side seal 222 furtherincludes a generally planar membrane portion 238 extends radially inwardfrom the annular shoulder bead 234. As an example, the bearing side seal222, particularly the membrane portion 238, may be constructed of asheet of adhesive-backed polyester material mounted on the bead 234. Thebearing side seal 222 may have a mechanical stiffness derived fromradial tensioning of the seal, back support from the axial bearingstator 130, or both.

The pump 10 further includes a PM motor side radial bearing structure250 connectable with the motor stator housing 22 and a PM bearing sideradial bearing structure 252 connectable with the bearing housing 24.The motor side radial bearing structure 250 and the bearing side radialbearing structure 252 may be similarly or identically configured. In theillustrated embodiment, each of the radial bearing structures 250 and252 includes a generally cylindrical PM bearing portion 254 and anannular flange portion 256 that extends radially outward from the PMbearing portion 254. The radial bearing structures 250 and 252 couldhave alternative configurations. The diameter and radial thickness ofthe PM bearing portions 254 may be similar or identical to that of themotor side radial bearing ring 60 and bearing side radial bearing ring80. The PM bearing portions 254 may be made of a permanent magnetmaterial with high coercivity such as neodymium boron iron. Also, the PMbearing portions may include multiple magnet segments and may includeflux carrying material, such as iron, to aid in creating a desiredmagnetic flux path.

In an assembled condition of the pump 10, the motor stator assembly 120is fixed to the motor stator housing 22 and the bearing stator assembly130 is fixed to the bearing stator housing 24. The rotor 12 ispositioned in the pump chamber 102 of the volute housing 20 such thatthe motor side end wall 32 of the impeller structure 30, the motor PMring 50, and the motor side PM radial bearing ring 60 are positionedadjacent the motor side opening 106 of the volute housing. The ICB sideend wall 34 of the impeller structure 30, the axial bearing target 70,and the bearing side PM radial bearing ring 80 are positioned adjacentthe bearing side opening 108 of the volute housing 20.

The motor seal assembly 200 is positioned on the volute housing 20 withthe annular bead 210 of the motor side seal 202 received in the annularrecess 212 of the motor side surface 214. The membrane portion 216 ofthe motor side seal 202 extends radially inward across the motor sideopening 106 of the volute housing 20. The tubular port 204 projects fromthe motor side seal 202 along the axis 16. The motor stator housing 22is positioned on the motor side surface 214 such that the port 204extends through a central opening 260 of the motor stator housing.

The O-ring 224 is placed in the annular groove 230 of the volute housing20 and the bearing side seal 222 is placed on the volute housing suchthat the O-ring is received in the annular groove 226. The bearingstator housing 24 is then placed on the bearing side surface 232 of thevolute housing 20 such that the annular bead 234 of the bearing sideseal 222 is received in the recess 236 of the bearing stator housing.The membrane portion 238 of the bearing side seal 222 extends radiallyinward across the bearing side opening 108 of the volute housing 20.

Fastening means 262, such as machine screws, are used to secure themotor stator housing 22 and bearing stator housing 24 to the volutehousing 20. This clamps the motor side seal 202 between the motor statorhousing and the volute housing. This also clamps the bearing side seal222 between the bearing stator housing and the volute housing. In theassembled condition of the pump 10, the bearing side seal assembly 200isolates the motor stator assembly 120 from the pump chamber 102 and thebearing side seal assembly 220 isolates the bearing stator assembly 130from the pump chamber.

In the illustrated embodiment, the motor side radial bearing 250 isconnected to the motor stator housing 22 via means 270, such as machinescrews, that extend through the flange portion 256 of the motor sideradial bearing. Also, in the illustrated embodiment, the bearing sideradial bearing 252 is connected to bearing housing 24 via means 272,such as machine screws, that extend through the flange portion 256 ofthe motor side radial bearing. Alternative means may be used to securethe radial bearings 250 and 252 to the housing 12.

The pump 10 illustrated in FIGS. 1 and 2 is configured to have reusableparts and disposable parts. This may be a desirable configuration, forexample, in the case of a non-implantable blood pump for short-term ormedium-term use, such as an assist pump for use in abridge-to-transplant or bridge-to-recovery scenario. This configurationis provided by the inclusion of the motor side seal assembly 200 and thebearing side seal assembly 220.

The motor side seal assembly 200 isolates the motor stator assembly 120and the motor stator housing 22 from the pump chamber 102 and from anyfluids (e.g., blood) in the pump chamber. Thus, during use of the pump10, the motor stator assembly 120 and the motor stator housing 22 arenot exposed to pumped fluids and thus may be reusable. Similarly, thebearing side seal assembly 220 isolates the bearing stator assembly 130and the bearing stator housing 24 from the pump chamber 102 and frompumped fluids in the pump chamber. Thus, during use of the pump 10, thebearing stator assembly 130 and the bearing stator housing 24 are notexposed to pumped fluids and thus may be reusable. During use of thepump 10, the volute housing 20, rotor 12, motor side seal assembly 200,and bearing side seal assembly 220 are exposed to pumped fluids and thusmay be disposable.

The pump 10 illustrated in FIGS. 1 and 2 may also be configured as adisposable pump that has no reusable parts. This may be a desirableconfiguration, for example, in the case of an-implantable pump formedium-term or long-term use, such as a heart replacement pump. In thisconfiguration, the motor side seal assembly 200 and the bearing sideseal assembly 220 may not be required to isolate motor stator assembly120 and motor stator housing 22 from the pump chamber 102. Similarly, inthis configuration, the bearing side seal assembly 220 may not berequired to isolate the bearing stator assembly 130 and the bearingstator housing 24 from the pump chamber 102. Thus, in the case where thepump 10 is disposable, the motor side seal assembly 200 and bearing sideseal assembly 220 may not be necessary and can be omitted. In thisinstance, means, such as O-rings or gaskets, may be used to form a sealbetween the motor side housing 22 and the volute housing 20 and betweenthe bearing side housing 24 and the volute housing. Also, in thisinstance, the inlet port 204 can be formed integrally with the motorside housing 22, can be fixed to the motor side housing by separatefastening means, or can be fixed to the motor side housing along withthe motor side radial bearing 250.

The operation of the pump 10 is essentially the same, regardless ofwhether the pump is disposable or has reusable parts. The maindifference between the configurations is a possible change in theeffective magnetic gap between the magnets of the axial and radialbearings caused by the presence or absence of the motor seal assembly200 and bearing seal assembly 220.

Referring to FIG. 2, a motor portion 280 of the pump 10 includes themotor stator assembly 120, the motor side end wall 32 of the rotor 12,and the motor PM ring 50. In the illustrated embodiment, the motorportion 280 is an eight pole, one sided axial gap permanent magnetbrushless DC motor. The motor portion 280 has six motor stator coils 122arranged for three phase excitation via, for example, a sinusoidalvoltage source. It will be appreciated that alternative configurationsfor the motor portion 280 may also be implemented.

Also, referring to FIG. 2, a motor side radial bearing 282 of the pump10 includes the motor side PM radial bearing ring 60 on the rotor 12 andthe PM motor side radial bearing structure 250 on the motor statorhousing 22. A bearing side radial bearing 284 of the pump 10 includesthe bearing side PM radial bearing ring 80 on the rotor 12 and the PMbearing side radial bearing structure 252 on the bearing stator housing24. An axial bearing 286 of the pump 10 includes the axial bearingtarget 70 on the rotor 12 and the ICB bearing stator assembly 130 on thebearing stator housing 24.

The pump is illustrated schematically in FIG. 6A. Referring to FIG. 6A,the magnets of the motor side and bearing side radial bearings 282 and284 are arranged symmetrically with each other along the axis 16. Themagnets of the radial bearings 282 and 284 are magnetized in the axialdirection (e.g., along the axis 16) and arranged such that the magnetsof each bearing are concentric with each other and attract each other.Thus, the motor side radial bearing ring 60 and the motor side radialbearing structure 250 are concentric with each other and attract eachother. The bearing side radial bearing ring 80 and the bearing sideradial bearing structure 252 are concentric with each other and attracteach other. As a consequence, if the magnets of either radial bearing282 and 284 become displaced radially from each other, the mutualattraction of the magnets in the axial direction will create a radialcomponent force that tends to return the magnets to their concentricequilibrium position. This can be described as a “radial stiffness” ofthe radial bearings. The radial bearings 282 and 284 thus help maintainthe radial position of the rotor 12 relative to the pump housing 14 andrelative to the axis 16.

The axial bearing 286 helps control the axial linear and tilt positionsof the rotor 12 relative to the pump housing 14. The position of therotor 12 may be affected by a variety of factors, such as axial forcesimposed on the rotor by the radial bearings 282 and 284, axial forcesimposed by the motor portion 280 of the pump 10, fluid flow through theimpeller structure 30, and gravity. The axial bearing 286, beingconfigured for independent three phase excitation in either the threecoil configuration (FIG. 4B) or six coil configuration (FIG. 4A), helpscontrol the axial position of the rotor 12 along the axis and the tiltposition of the rotor relative to the axis. To control the position ofthe rotor 12 along the axis 16, all three phases may be excited equally.To control the tilt position of the rotor 12 relative to the axis 16,the phases may be excited at different magnitudes.

The axial bearing 286 is configured such that excitation of the bearingstator coils 132 causes the coils and the axial bearing target 70 toattract each other. Excitation of the axial bearing 286 thus imposes anaxial force on the rotor 12 that attracts the rotor toward the bearingstator assembly 130. The radial bearings 282 and 284 are configured toimpose a net axial force on the rotor 12 in a direction opposite thatimposed by the axial bearing 286. The position of the rotor 12 may thusbe controlled via excitation of the axial bearing 286 to help maintainthe rotor 12 in a desired levitated position.

Excitation of the axial bearing 286 is controlled via tuned LCR bearingcircuits. There are three such LCR bearing circuits, one associated witheach of the axial bearing stator poles 132 a-c (see FIGS. 4A and 4B).The LCR bearing circuits provide three phase excitation of the axialbearing stator 130. Each of the three LCR bearing circuits can beidentical, with the exception of the difference of phase shift betweenthe circuits. Each axial bearing stator pole 132 a-c acts as anelectromagnet when excited and thereby attracts the axial bearing target70.

FIG. 6A depicts an example of a tuned LCR bearing circuit 300illustrative of the circuit associated with each of the three axialbearing stator poles 132 a-c. Each LCR bearing circuit 300 includes acoil 132 of an associated one of the bearing stator poles 132 a-cconnected in series with a capacitor 302, a resistor 304, and a voltagesource 306. The resistor 304 could be in the form of a separate resistorcomponent, the inherent resistance of the bearing stator poles, or both.The bearing stator poles 132 a-c each have an inductance (L), thecapacitor 302 has a capacitance (C), and the resistor 304 has aresistance (R). The voltage source 306 produces a sinusoidal voltage (E)that excites its associated bearing stator pole. The voltage (E) has afixed frequency (ω) that is slightly above a resonant frequency (ω_(R))of the circuit 300. The frequency (ω) used in the LCR bearing circuit300 for each coil 132 of the axial bearing 286 may be different. Also,for each LCR bearing circuit 300, different frequencies (ω) may be usedfor start-up and steady state conditions of the pump 10.

As shown in FIG. 6A, the LCR circuit 300 is used to help suspend therotor 12 via excitation of its associated bearing stator pole 132 a-c ofthe axial bearing 286. According to the present invention, the LCRcircuit provides self-sensing and self-positioning magnetic suspensionof the rotor 12. The self-sensing and self-positioning magneticsuspension of the rotor 12 is illustrated in the force versus gap plotof FIG. 6B. Referring to FIGS. 6A and 6B, if the rotor 12 moves awayfrom the bearing stator 130, the magnetic gap 310 between the bearingstator and the axial bearing target 70 on the rotor increases and theinductance (L) decreases. As a result, the resonant frequency (ω_(R)) ofthe circuit 300 increases, thus becoming closer to the excitationfrequency (ω) of the circuit. This causes an increase in the AC currentgenerated by the voltage source 306, which increases the force withwhich the associated bearing stator pole 132 a-c attracts the rotor 12.As a result, the axial force imposed on the rotor 12 pulls the rotortoward the associated bearing stator pole.

If the rotor 12 moves toward the bearing stator 130, the magnetic gap310 decreases and the inductance (L) increases. As a result, theresonant frequency (ω_(R)) of the circuit 300 decreases, thus increasingthe difference between the resonant frequency and the excitationfrequency (ω). This causes a decrease in the AC current generated by thevoltage source 306, which decreases the force with which the bearingstator pole 132 a-c attracts the rotor 12. As a result, the axial forceimposed on the rotor 12 by the bearing stator pole 132 a-c is reducedand the axial force imposed on the rotor by the radial bearings 282 and284 pulls the rotor away from the bearing stator 130. It will thus beappreciated that the LCR circuits 300 help maintain a fixed gap 310between the bearing stator poles 132 a-c and the axial bearing target 70and helps maintain the position of the rotor 12.

It will also be appreciated that the excitation current may be used asan indication of the position of the rotor 12. This is because, asdescribed above, the excitation current of the axial bearing 286 isproportional to the magnetic gap between the bearing stator 130 and theaxial bearing target 70. Also, since the poles 132 a-c of the axialbearing 286 control both the axial and tilt positions of the rotor 12,the excitation currents may be used to determine both the axial positionof the rotor and the tilt position of the rotor.

The coils 122 of the motor stator 120 are excited via sinusoidal voltagesource 292 shown schematically in FIG. 6A, which produces rotation ofthe rotor 12 and pumping action of the pump 10 in a known manner. Thefluid to be pumped is drawn into the pump housing 14 (FIG. 2) throughthe inlet 26 and is directed through the impeller passages 38 into thepump chamber 102. The fluid fills the pump chamber 102 and is directedthrough the outlet 28 via the pumping channel 104.

The coils 122 of the motor stator 120 are excited with a signal having afrequency in the megahertz range via the sinusoidal voltage source 292.The coils 132 of the bearing stator 130 are excited with a signal havinga frequency in the hundreds of hertz range via the sinusoidal voltagesource 306. Those skilled in the art will appreciate that it may bedesirable to superimpose the power for the bearing stator coils 132 onthe power for the motor stator coils 122. The motor would thus require asingle set of power leads. The power could be low pass filtered to thebearing stator coils 132 and either fed directly to or high passfiltered to the motor stator coils 122.

During operation of the pump 10, the fluid in the pump chamber 102 mayprovide damping for the rotor 12. More particularly, squeeze filmdamping may occur between the rotor 12 and the motor stator assembly 120and between the rotor and the bearing stator assembly 130. The motorside end wall 32 and bearing side end wall 34 of the rotor may beconfigured to have a generally flat, smooth surface presented toward themotor stator and bearing stator assemblies 120 and 130, respectively.The opposing surfaces of the motor stator assembly 120 and the motorside end wall 32 and the opposing surfaces of the bearing statorassembly 130 and the bearing side end wall 34 and bearing statorassembly 130, being large, flat, smooth, and closely spaced, may helppromote the squeeze film damping of the rotor 12.

In the illustrated embodiment, including the six bearing stator coil 132configuration of the bearing stator 130 illustrated in FIG. 4B, theaxial bearing stator core 134 may be fabricated by winding a thin flatstrip of material in a spiral to form a cylinder. The cylinder is thenmachined to form the six stator posts 136 around which the wire is woundto form the coils 132. The axial bearing target 70 may have a similarwound construction. The flat strips of material used to form the axialbearing stator core 134 and axial bearing target 70 can have a highmagnetic permeability. For example, the flat strips may be formed of aferrite, powder iron, or laminated silicon steel.

The adjacent coils 132, wound in opposite directions with the same wire,induce magnetic flux in opposite axial directions in their respectivestator posts 136. The oppositely wound coils 132 reduce the mutualinductance between the three bearing stator poles 132 a-c. This allowsthe bearing stator poles 132 a-c to operate without mutually interferingwith each other. This configuration helps reduce the likelihood that achange in current in one of the bearing stator poles 132 a-c due to achange in the magnetic gap 310 (see FIG. 6A) over that particular polewill result in inducing a change in current and force in the other twobearing stator poles.

The axial bearing stator assembly 130 and the axial bearing target 70are important elements in the design of the axial bearing 286. It may bedesirable that the material used to construct the axial bearing statorcore 134 have a high saturation flux density so that the axial forcedensity (i.e., the force per unit of stator volume) capability of thestator assembly 130 is high. It is also desirable the magneticpermeability of the material used to construct the stator core 134 ishigh to help keep low the coil losses of the axial bearing 286. If themagnetic permeability of the stator core 134 is low, then additionalamp-turns must be generated by the axial bearing coils 132 to induce therequired level of magnetic flux density in the air gap between thestator 130 and the axial bearing target 70. Higher coil amp-turnsrequire either more current through the same number of coil turns, orthe same current though a larger number of coil turns. In either case,the coil i²R (power) loss associated with a given coil geometry isincreased.

It may also be desirable that the axial bearing stator 130 be operatedat a flux density sufficiently far removed from magnetic saturation tohelp avoid detrimental effects on axial bearing behavior that can resultfrom permeability non-linearities that typically accompany the approachto magnetic saturation. The typical rapid decrease in magneticpermeability results in a corresponding decrease in stator leg air gapflux density with an associated decrease in coil self-inductance. In asense, the decrease in permeability as a material approaches saturationcan have an effect similar to an increase in stator to target air gap.Consequently, the rapid drop in permeability as the stator materialapproaches magnetic saturation can significantly alter the shape of theforce characteristic curve shown in FIG. 6B, and can result in thebearing being inoperative.

Those skilled in the art will appreciate that the axial bearing statorcore 134 can be made from a variety of magnetic materials, such as aferrite material, a sintered iron material, or a high performancemetallic lamination. Ferrite materials typically have a low saturationflux density (typically 0.4 to 0.5 Tesla), which can limit the fluxdensity generated in the stator to target air gap and thereby can limitthe force density of the axial bearing 130. Sintered iron material has aflux saturation flux density (typically 0.8 Tesla) greater than that ofthe ferrite material, but also has a low permeability. The lowerpermeability of the sintered iron material may require that a high coilcurrent be used in order to take advantage of the higher flux densitycapability of the sintered iron material. This, however, can result inhigher coil i²R losses. A laminated stator material may have both highflux density and high permeability. For example, a silicon steel orcobalt iron alloy material can be used to construct an axial bearingstator 130 with both high force density and low coil loss.

High performance metallic stator materials tend to be good electricalconductors and their use in electrical equipment operating at highfrequencies such as those used in the axial bearing 286 may necessitatethat the stator materials be laminated in order to reduce eddy currentlosses. In doing so, it may also be desirable to laminate the statormaterial in a manner consistent with low manufacturing cost. This can beachieved in various manners. For example, the stator materials may belaminated with tapered radial laminations, with laminations bent in acurve similar to a logarithmic spiral, or by spiral winding a thin stripof magnetic material about a cylindrical mandrel into a cylinderpre-machined stator precursor. Spiral winding may be more desirable thantapered laminations and bent curve laminations since the magnetic fluxtends to be directed in the circumferential direction in the flux pathof the target and in the regions of the stator below the excitationcoils.

In an example configuration, the spiral winding approach was used forthe fabrication of both the axial bearing stator core 134 and the axialbearing target 70. For the stator core 134, a thin 0.004″ by 0.5″ wideby 290″ long strip of silicon iron was spiral wound about a 0.70″diameter cylindrical mandrel to form a stator precursor. After removalfrom the mandrel, the upper and lower faces of the resulting spiralwound stator precursor were machined flat. After this machining resultedin a stator cylinder of the correct height, coil slots defining thestator posts 136 were cut into the cylinder using a machining method,such as milling, grinding, or EDM machining. The latter method may bepreferable since it tends to eliminate smearing of lamination materialfrom lamination to lamination. This smearing can result in local shortcircuits between laminations which tend to defeat the purpose for usingseparate thin metallic laminations that are electrically insulated fromone another.

The axial bearing target 70 was fabricated in a similar fashion. A thin,long strip of silicon iron spiral was wound around a cylindrical mandrelto form a target precursor. After removal from the mandrel, the upperand lower faces of the resulting spiral wound target precursor weremachined flat to form the target 70. Since the target 70 is in the shapeof a simple washer, no additional machining was required after machiningits upper and lower surfaces flat and to the associated proper washerheight.

Thus far, the pump 10 has been illustrated as having a dual radialbearing configuration including the motor side radial bearing 282 andthe bearing side radial bearing 284. The pump 10 could, however, beconfigured to have a single radial bearing. In this instance, forexample, the bearing side radial bearing 284 could be omitted and themotor side radial bearing 282 could be configured to provide the desiredradial stiffness and axial pull to oppose the axial bearing 286. Asanother example, the motor side radial bearing 282 could be omitted andthe bearing side radial bearing 284 could be configured to provide thedesired radial stiffness and axial pull to oppose the axial bearing 286.The dual radial bearing configuration, however, can help provide addedadjustability.

According to the present invention, the dual radial bearingconfiguration using the motor side radial bearing 282 and the bearingside radial bearing 284 allows for adjustment of the net axial forceimposed on the rotor 12 by the radial bearings independently from theadjustment of the radial stiffness imposed on the rotor by the radialbearings. According to the present invention, adjustment of the motorside radial bearing 282 and bearing side radial bearing 284 is achievedby adjusting the position of the PM motor side radial bearing structure250, the PM bearing side radial bearing structure 252, or both. Theseadjustments may be performed, for example, by adjusting the fasteningmeans 270 and 272 that are used to connect the motor side radial bearing250 and bearing side radial bearing 252 to the housing 14.

Adjustment of the motor side radial bearing 282 and the bearing sideradial bearing 284 is shown in FIGS. 5A-5C. Referring to FIG. 5A, themotor side radial bearing 282, i.e., the motor side PM radial bearingring 60 and the PM motor side radial bearing structure 250, and thebearing side radial bearing 284, i.e., the bearing side PM radialbearing ring 80 and the PM bearing side radial bearing structure 252,are illustrated schematically.

To adjust the radial stiffness of the bearings 282 and 284 independentlyof the net axial pull exerted on the rotor 12 by the bearings, the motorside radial bearing 250 and stator side radial bearing 252 are movedeither toward or away from each other in equal amounts. This is shown inFIG. 5B. Referring to FIG. 5B, to increase the radial stiffness of thebearings 282 and 284 without affecting the net axial pull exerted on therotor 12, the motor side and stator side radial bearings 250 and 252 aremoved equal distances toward each other. This is illustrated at 250′ and252′ in FIG. 5B. To decrease the radial stiffness of the bearings 282and 284 without affecting the net axial pull exerted on the rotor 12,the motor side and stator side radial bearings 250 and 252 bearings aremoved equal distances away from each other. This is illustrated at 250″and 252″ in FIG. 5B.

To adjust the net axial pull exerted on the rotor 12 by the bearings 282and 284 independently of the radial stiffness with which the bearingssupport the rotor, the motor side radial bearing 250 and stator sideradial bearing 252 are moved relative to the rotor with their positionrelative to each other remaining unchanged. Thus, in adjusting the netaxial pull, the motor side and stator side radial bearings 250 and 252are moved equal distances relative to the rotor 12, one bearing movingtoward the rotor and the other bearing moving away from the rotor. Thisis shown in FIG. 5C. Referring to FIG. 5C, to increase the net axialpull of the bearings 282 and 284 in the direction of the arrow in FIG.5C, the motor side and stator side radial bearings 250 and 252 are movedtoward the positions illustrated at 250′ and 250′ in FIG. 5C. Todecrease the net axial pull of the bearings 282 and 284 (i.e., increasethe net axial pull in the direction opposite the arrow in FIG. 5C), themotor side and stator side radial bearings 250 and 252 are moved towardthe positions illustrated at 250″ and 252″ in FIG. 5C. Because the axialforce and radial stiffness are non-linear functions relative to themagnet gap, independent adjustment is possible when the adjustments aresmall relative to the total gap between magnets (e.g., <20%). As theadjustments get larger than this, second-order effects are morepronounced, and the adjustments become less independent.

As a further feature of the radial bearing design of the presentinvention, the motor side radial bearing 282 and the stator side radialbearing 284 may be offset from each other to help negate an average nethydraulic radial force exerted on the rotor 12. More specifically, themotor side PM radial bearing ring 60, PM motor side radial bearingstructure 250, bearing side PM radial bearing ring 80, and the PMbearing side radial bearing structure 252 may be offset relative to eachother to exert a radial force on the rotor 12 opposite the average nethydraulic radial force. This may help the rotor 12 to run more centeredon the axis 16.

First Example Pump Configuration

In a first example configuration, a rotary pump is constructed inaccordance with the present invention. The first example pumpconfiguration is of the disposable configuration, omitting the bearingassembly seal and the motor assembly seal, as described above. For thefirst example pump configuration, each motor stator coil is made ofeight layers of 25-gage copper wire, and occupies 0.16-in. of space. Themotor magnets and coils are positioned on silicon-steel cores that serveas flux return paths. The cores are thin, with the intent to choke theflux to help minimize flux changes with motor gap changes. This helpsreduce the negative stiffness of the motor.

The flux density distribution was estimated using a two-dimensionalfinite element analysis program and the results indicate a calculatedpeak flux density of 0.25 tesla at the middle of the coil space. Usingan axial gap motor analysis program and assuming this sinusoidal peakflux density of 0.25 tesla, the calculated motor efficiency is 70% for5.3-W output at 2,700 rpm and 5 liter/min at 100 mm-Hg. Thus, the motorinput power will be 7.6 W (5÷0.70). Allowing approximately 2 W for axialbearing operation, the total power consumption for this first examplepump configuration is about 9.6 W. At the 4,300-rpm speed, the motorefficiency is about 70%, which equates to an overall power consumptionof about 20.6 W.

For a nominal magnetic gap of 0.19-in. from rotor magnet surface tostator core (0.030-in. walls/fluid gap plus 0.160-in. coil thickness),the axial pull of the motor was calculated to be 1.94 lb (F_(motor)).Reducing the gap by 0.005-in. increases this force to 2.07 lb. Usingthese values, the axial stiffness is calculated to be −26.0 lb/in.(K_(amotor)), and the angular stiffness is thus:K _(θmotor) =K _(amotor)(R _(o) ² +R _(i)²)/4=(−26.0)(0.75²+0.25²)/4=−4.06 lb-in./radThese values for motor stiffness are used in our estimation of rotorcritical speeds, as shown below.

In the first example pump configuration, a single radial bearing designis employed and the pump includes only a bearing side radial bearing, asdescribed above. The motor side PM radial bearing ring and the PM motorside radial bearing structure of the radial bearing are axial polarized(1.0-tesla remnant flux density) magnet rings with a 0.55-in. OD and asquare cross section of 0.1-in. Using a PM bearing analysis program, thestiffness and axial pull versus gap values are calculated as shown inTable 1. TABLE 1 Radial Bearing Force and Stiffness Gap, in. F_(calc,)lb K_(rcalc,) lb/in. K_(acalc,) lb/in. K_(θcalc,) lb-in./rad 0.03 2.0622.3 −44.5 −2.25 0.04 1.67 16.8 −33.6 −1.7 0.05 1.38 13.0 −26.0 −1.32

In the first example pump configuration, the bearing stator assembly hasthe three bearing stator coil configuration, as described above (seeFIG. 4B). The pole area per LCR circuit is approximately 0.190-in.², andthe coil slot radial width is 0.120-in. 200 turns of 32-gage copper wirewere used (0.008-in. copper diameter; 0.009-in. diameter with enamelinsulating coating). The slot depth is about 0.240-in. The wireresistance is approximately 6.9 ohm (R). For the rotor to operate at0.015-in. magnetic gap (walls plus fluid space), a tuning inductance of4.66×10⁻³ Henry (L) calculated at 0.013 in is selected. Using acapacitor of 2.5×10⁻⁶ Farad (C), the calculated resonance frequency ofthe LCR circuit is 1474 Hz (_(ωn)=9,257 rad/sec). The amplificationfactor of this resonance is approximately Q=L_(ωn)/R=6.2.

The response peak is wide enough to accommodate 0.010-in. of rotor axialdisplacement. The rotor should be confined in the axial displacementrange of ±0.005-in. from the operating gap at 0.015-in. The firstexample pump configuration allowed 0.010-in. of fluid flow space and0.005-in. walls. In this range, the average axial stiffness was 26lb/in. per LCR circuit, or a total of 78 lb/in.

The weight of the rotor 12 is estimated to be about 0.083 lb. At thepreset gap of 0.013-in the axial pull per LCR is calculated to be 0.08lb for a total of 0.24 lb. The steady-state force balance requires:F _(calc)=−3F _(lcr) +F _(motor) −Mg=−0.24+1.94−0.083=1.617 lbThis assumes that the motor is on top and the impeller weight actsagainst the motor pull. By interpolation from rows 2 and 3 of Table 1,the radial bearing gap will be 0.042-in., and the stiffness of theradial bearing is K_(rcalc)=16.1 lb/in., K_(acalc)=−32.2 lb/in. andK_(θcalc)=−1.63 lb-in./rad. The sum of motor and radial bearing negativeaxial stiffness is 58.2 lb/in. (=26.0+32.2), which is less than thetotal axial bearing positive axial stiffness (78 lb/in.). Similarly, theaxial bearing provides more angular stiffness, i.e., 11.0 in.-lb/rad(=1.5×26×0.5312) than the total negative angular stiffness of the motorand radial bearing. This result ensures that there is sufficient forceand axial and angular stiffness to levitate and support the rotor.

The analysis indicates a power loss of 0.67 W for each of the bearingLCR circuits, or 2.0 W total for the three bearing LCR circuits of theaxial bearing stator. The corresponding coil peak current is 0.44 A,which corresponds to a coil slot current density of:J=(0.44)(200)/(0.12)(0.24)=3056 A/in ²=4.7 A/mm ²This coil slot current density is an acceptable value with nominalamounts of fluid cooling.

As described above, the weight (M) of the rotor 12 will be 0.083 lb. Therotor inertias are:Polar moment of inertia: I _(p) =MR ²/2=(0.083)(0.75)²/2=0.0233 lb-in. ²

Transverse moment of inertia: I_(t)=M(R²/4+L²/12)=0.0128 lb-in.²; forL=0.4-in.

Because, in the first example pump configuration, the radial bearing isat only one side of the rotor, the lateral and rocking modes have mixedmode shapes, i.e., mixing with both radial and rocking motions. Usingthe above mass inertial and stiffness data, we calculated the first(radial dominating) critical speed at 2,600 rpm and a very high second(rocking dominated) critical speed due to the gyroscopic effect. Theaxial critical speed is determined to be 2,900 rpm.

The critical speeds will be influenced by the effective mass added tothe impeller as a result of its motion within the fluid being pumped.For a blood pump, the added masses for blood are:Radial mode: M _(ra)=_(ρπ) R ² L=0.027 lbAxial mode: M _(aa)=(8/3)_(ρ) R=0.043 lbThese values are significant portions of the estimated rotor mass of0.083 lb. Their effect will be to lower the critical speeds to 2,258 rpm(radial) and 2,354 rpm (axial). These two calculated critical speeds arerespectively 16% and 13% lower than the lower operating speed (2,700rpm). The calculated critical speeds could be detuned to be acceptableby slightly reducing the stiffness. Damping in the rotor dynamic systemmay also help traverse the critical speed.

The first example pump configuration exhibited sufficient stiffness inthe bearing system to resist imposed shock and vibration loads. Bearingpower consumption was below 2.5 W at all operating conditions. The pumpexhibited the ability to pump 5 liter/min at 100 mm-Hg pressure rise,with a motor input power below 8 W. The pump also exhibited the abilityto pump 4 liter/min at 350 mm-Hg pressure rise, with motor power below25 W. The pump further exhibited the ability to pump 9 liter/min, 120mm-Hg pressure rise, with 40-W maximum power.

The first example pump configuration, described above and constructed inaccordance with the present invention, provided high stiffness, goodpower efficiency, and high reliability without position sensors oractive feedback electronics. The inclusion of the LCR axial bearingstructure helps eliminate the need for a shaft seal and helps provide aclean wash flow patterns. In a blood pump implementation, this will helpreduce the rate of thrombus formation in the pump. The magnetic axialbearing is also more durable than the ball bearings or bushings. Therelatively small size of the pump in the first example configuration(6.4 cm diameter by 3.2 cm thick) may also be desirable.

Second Example Pump Configuration

In a second example configuration, a rotary pump is constructed inaccordance with the present invention. The second example pumpconfiguration is of the reusable configuration and thus includes thebearing assembly seal and the motor assembly seal, as described above.The motor stator assembly and axial bearing stator assembly of thesecond example pump configuration are reusable. For the second examplepump configuration, the pump includes an axial bearing having the sixcoil configuration of FIG. 4A. Also, the rotor diameter is decreased to1.5 inches in order to reduce viscous drag losses by more than theresulting speed increase, and in order to reduce the motor torque outputrequired for a particular hydraulic output.

The 6-pole stator core for the axial bearing of the second example pumpconfiguration is made of laminated steel. A flat strip or strips oflaminated silicon-steel are wound to form an axial bearing target thatis fixed to the rotor. As an example, a strip of laminated silicon-steelthat is 0.1-mm thick and 3.0-mm wide may be wound to form a 3.0-mm thickaxial bearing target on the rotor. Thin-film barriers are used to formthe motor seal and bearing seal assemblies that seal the motor statorand axial bearing stator from the rotor. On the motor side, the volutedesign from the implantable pump is modified to accommodate the annularbead in the form of a machined polycarbonate ring. A 20-mil-thick (0.25mm) sheet of polycarbonate forming the membrane portion is glued to thering and the inlet port is glued to the polycarbonate sheet. On thebearing side, a 2-mil-thick (0.05 mm) sheet of adhesive-backed polyestermaterial forming the membrane portions is mounted on a metal ringforming the annular bead and the assembly is secured in the statorhousing with an O-ring to seal the axial bearing stator from the rotor.

In the second example configuration of the pump, the axial-gap motor hasa measured power capacity of 27 W and a torque constant of approximately0.01 Nm/A. The entire motor core, including the posts, is made ofpowdered iron so as to reduce eddy current loss. The iron posts form apart of the flux return path formed by the core of the motor. Withoutthe posts, the magnetic flux would flow evenly between the magnets andthe core. With the posts, the flux tends to concentrate and pass throughthe bearing coils. In this way, the posts serve to increase the magneticflux link of the coils and thus produce more torque per unit of coilcurrent. Since the motor PM ring on the rotor has eight poles, themagnetic flux in the core fluctuates at a frequency of 500 Hz or higher.

The poles on the core may also increase the negative axial and angularstiffness on the rotor. The negative axial stiffness can be compensatedfor by the use of higher coil currents. Maintenance of the angularstiffness requires more “moment arm,” or radial distance between thebearing poles and bearing center, because the positive angular stiffnessis proportional to the square of the distance. Therefore, to compensatefor the angular stiffness by increasing the moment arm, the bearing corepole areas in the ICB were moved out radially.

Laminated silicon steel is used to form the axial bearing stator and theaxial bearing PM ring on the rotor. In the second example pumpconfiguration, the dual radial bearing design (see FIGS. 5A-5C) isemployed. The second example pump configuration thus includes both amotor side radial bearing and a bearing side radial bearing.

During testing, the second example pump configuration was run safely ata maximum power of approximately 40 W without overheating the motorcoils. Loss data was calculated from observed peak-to-peak values of thebearing sinusoidal currents, and the coil resistance of 3.8 ohms per LCRbearing circuit. The maximum recorded bearing power loss is identifiedas 1.7 W. Considering the eddy current and hysteresis loss oflaminated-silicon-steel bearing cores, it was observed that, atapproximately 900 Hz (the LCR bearing circuit excitation frequency) andan average estimated flux density of 4 kilogauss in the cores, the lossis approximately 1.0 W/lb of core material. Since the second examplepump configuration includes about 0.12 lb of laminated cores, anadditional loss of 0.12 W was estimated. Therefore, the total bearingloss for the second example pump configuration for all operatingconditions is calculated at no more than 1.82 W (1.7+0.12).

With shocks imposed at 32-g in the axial direction and 42-g in thevertical direction loads, the LCR bearing circuit currents showedinsignificant response. The second example pump configuration thusdemonstrates sufficient stiffness in the radial and axial bearings. Thepump also exhibited the ability to pump 5 liter/min at 100 mm Hgpressure rise, with motor power input below 8 W; the ability to pump 4liter/min at 350 mm Hg pressure rise, with motor power below 25 W; andthe ability to pump 9 liter/min, 120 mm Hg pressure rise, with 40-Wmaximum power.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. Suchimprovements, changes and modifications within the skill of the art areintended to be covered by the appended claims.

1. A pump comprising: a housing having a fluid inlet and a fluid outlet;a rotor disposed within the housing and rotatable about an axis to movefluid from the fluid inlet to the fluid outlet; and a magnetic axialbearing for supporting the rotor, the axial bearing comprising an axialbearing target disposed on the rotor and an axial bearing statordisposed on the housing, the axial bearing stator including multiplestator poles, each of the stator poles including a first coil portionwound in a first direction and a second coil portion wound in a seconddirection opposite the first direction.
 2. The pump recited in claim 1,wherein the first and second coil portions are formed from a singlelength of wire.
 3. The pump recited in claim 1, wherein the firstdirection is clockwise and second direction is counterclockwise.
 4. Thepump recited in claim 1, wherein each of the multiple stator poles isexcited by an electrical phase of a multiple phase voltage source. 5.The pump recited in claim 1, wherein each of the multiple stator polescomprises an electromagnet having an inductance (L), the electromagnetbeing connected in series with a resistance (R), a capacitance (C), anda phase voltage source to form an LCR circuit for controlling the axialbearing.
 6. The pump recited in claim 1, wherein the bearing stator isexcitable to attract the axial bearing target and the rotor.
 7. The pumprecited in claim 1, wherein the bearing stator includes three statorpoles, each stator pole including a first coil wound in a clockwiseconfiguration and a the second coil wound in a counterclockwiseconfiguration, each of the stator poles being excited by a correspondingelectrical phase of a three phase voltage source.
 8. The pump recited inclaim 7, wherein the first and second coils are wound with a singlelength of wire.
 9. The pump recited in claim 1, wherein the axialbearing stator comprises a strip of material wound in a cylindrical coiland machined to form a stator core including stator posts around whichthe first and second coils of each stator pole are wound.
 10. The pumprecited in claim 9, wherein the strip of magnetic material comprises oneof a ferrite, powdered iron and laminated silicon steel material. 11.The pump recited in claim 1, further comprising: a magnetic first radialbearing for exerting a force on the rotor in a first direction along theaxis; and a magnetic second radial bearing for exerting a force on therotor in a second direction along the axis opposite the first direction;the first and second radial bearings being adjustable to allow foradjusting the net axial force exerted on the rotor by the radialbearings independent of the radial stiffness of the radial bearings. 12.A pump comprising: a housing having a fluid inlet and a fluid outlet; arotor disposed within the housing and rotatable about an axis to movefluid from the fluid inlet to the fluid outlet; a magnetic first radialbearing for exerting a force on the rotor in a first direction along theaxis; and a magnetic second radial bearing for exerting a force on therotor in a second direction along the axis opposite the first direction;the first and second radial bearings being adjustable to allow forindependently adjusting the net axial force exerted on the rotor by theradial bearings and the radial stiffness of the radial bearings.
 13. Thepump recited in claim 12, wherein one of the first and second radialbearings is adjustable an axial distance toward the rotor and the otherof the first and second radial bearings is adjustable the same axialdistance away from the rotor to adjust the net axial force exerted onthe rotor by the first and second radial bearings independent of theradial stiffness of the first and second radial bearings.
 14. The pumprecited in claim 13, wherein the first and second radial bearings areadjustable an equal axial distance toward the rotor to increase theradial stiffness of the first and second radial bearings independent ofthe net axial force exerted on the rotor by the first and second radialbearings.
 15. The pump recited in claim 13, wherein the first and secondradial bearings are adjustable an equal axial distance away from therotor to vary the radial stiffness exerted of the first and secondradial bearings independent of the net axial force exerted on the rotorby the first and second radial bearings.
 16. The pump recited in claim12, wherein the first radial bearing comprises a first magnetic ringsupported on the housing facing a first side of the rotor and a secondmagnetic ring supported the housing facing a second side of the rotor,opposite the first side of the rotor, the first and second magneticrings being adjustable along the axis to independently adjust the netaxial force exerted on the rotor by the radial bearings and the radialstiffness of the radial bearings.
 17. The pump recited in claim 16,wherein the first radial bearing further comprises a third magnetic ringon the first side of the rotor and the second radial bearing furthercomprises a fourth magnetic ring on the second side of the rotor, thefirst and third magnetic rings being arranged to attract each other, thesecond and fourth magnetic rings being arranged to attract each other.18. The pump recited in claim 17, wherein the first, second, third andfourth magnetic rings are centered on the axis.
 19. The pump recited inclaim 17, wherein the magnetic rings are offset in order to oppose anaverage net hydraulic radial force exerted on the rotor by the fluid.20. The pump recited in claim 1, wherein the axial bearing stator isexcited by voltage superimposed on a voltage supplied to a motor statorof the pump.
 21. A pump comprising: a housing having a fluid inlet and afluid outlet; a rotor disposed within the housing and rotatable about anaxis to move fluid from the inlet to the outlet, the rotor comprisingpermanent magnets arranged on a first side of the rotor and amagnetically conductive disk arranged on a second side of the rotoropposite the first side of the rotor; a motor stator arranged on thehousing to interact with the permanent magnets on the rotor; at leastone electromagnet arranged on the housing to interact with themagnetically conductive disk on the rotor; and at least one ring magnetarranged on at least one of the first and second sides of the rotor; atleast one ring magnet arranged on the housing to magnetically interactwith the at least one ring magnet on the rotor.
 22. The pump recited inclaim 21, wherein the interaction between the motor stator and thepermanent magnets on the rotor, and the interaction between the at leastone electromagnet and the magnetically conductive disk on the rotorcombine to suspend the rotor on the axis.
 23. The pump recited in claim21, wherein the electromagnet comprises a stator, the stator comprisingone of an oriented and a non-oriented surface insulated electromagneticlamination material that is spiral wound.
 24. The pump recited in claim23, wherein comprising pole shapes are cut into the spiral woundmaterial so as to be free from short circuits between layers of thespiral wound material.
 25. The pump recited in claim 21, wherein the atleast one electromagnet comprises coils having a common ground.
 26. Thepump recited in claim 21, wherein the at least one electromagnetcomprises a plurality of coils wound in alternating directions.
 27. Thepump recited in claim 26, wherein adjacent pairs of the coils are woundwith a single length of wire.
 28. The pump recited in claim 26, whereinthe coils have an inductance L and are connected with a resistance R anda capacitance C.
 29. The pump recited in claim 26, wherein the coils areexcited with an alternating current.
 30. The pump recited in claim 29,wherein each coil is excited with a different frequency of alternatingcurrent.
 31. The pump recited in claim 29, wherein the magnitude of thealternating current is used as an indicator of rotor position.
 32. Thepump recited in claim 29, wherein two different frequencies are used toexcite the coils, one of the frequencies during start-up, and another ofthe frequencies during steady state operation.
 33. The pump recited inclaim 26, wherein the coils have an inductance that varies with themotion of the rotor, the current flow through the coils varying with theinductance of the coils.
 34. The pump recited in claim 33, wherein thechanges in current flow result in changes in electromagnetic force thatoppose the rotor motion.
 35. The pump recited in claim 21, wherein rotorvibrations are dampened by pumped fluid between the rotor and the motorstator and between the rotor and the electromagnet.
 36. The pump recitedin claim 35, wherein close clearances between the rotor and motor statorand between the rotor and the electromagnet impede fluid flow toincrease damping effects.
 37. The pump recited in claim 36, wherein oneof the close clearances is between the adjacent radii at an inlet of therotor.
 38. The pump recited in claim 21, wherein the ring magnets on therotor and the ring magnets on the housing are positioned symmetricallywith each other.
 39. The pump recited in claim 38, wherein the ringmagnets on the first side of the rotor, ring magnets on the second sideof the rotor, ring magnets on the motor stator, and ring magnets on theelectromagnet are positioned symmetrically with each other.
 40. The pumprecited in claim 38, wherein at least one of the ring magnets on themotor stator and the electromagnet are adjustable to tune radial andaxial components of force.
 41. The pump recited in claim 21, wherein atleast one of the ring magnets is adjustable to tune radial and axialcomponents of force.
 42. The pump recited in claim 21, wherein thehousing comprises a sealed cartridge with separately removable andreusable motor and stator housings.
 43. The pump recited in claim 42,further comprising at least one sealing wall that has a mechanicalstiffness derived from a combination of radial tension and back supportfrom the removable stator housings.
 44. The pump recited in claim 21,wherein the magnetically conductive disk on the rotor is formed from aspiral wound lamination material.
 45. The pump recited in claim 21,further comprising a projection for directing flow into the rotor flowpath, the projection forming a stop point for excessive axial rotortravel.
 46. A pump comprising: a housing having a fluid inlet and afluid outlet; a rotor disposed within the housing and rotatable about anaxis to move fluid from the inlet to the outlet; a motor arranged tocause rotation of the rotor; at least one electromagnet arranged tointeract magnetically with material in the rotor, the electromagnetcomprising a stator formed from a spiral wound lamination material. 47.A pump comprising: a housing having a fluid inlet and a fluid outlet; arotor disposed within the housing and rotatable about an axis to movefluid from the inlet to the outlet; a motor arranged to cause rotationof the rotor; at least one electromagnet arranged to interactmagnetically with material in the rotor, the electromagnet comprising aneven number of poles, adjacent poles being wound in opposite directions.48. The pump recited in claim 47, wherein adjacent poles are arranged inpairs and are wound with a single length of wire.
 49. A pump comprising:a housing having a fluid inlet and a fluid outlet; a rotor disposedwithin the housing and rotatable about an axis to move fluid from theinlet to the outlet; a motor arranged to cause rotation of the rotor; atleast one electromagnet arranged to interact magnetically with materialin the rotor, the material comprising a disk of spiral wound magneticalloy material.
 50. A method for magnetically supporting a pump rotor ina housing for rotation about an axis, the method comprising the stepsof: providing an axial bearing target on the rotor; providing an axialbearing stator on the housing, the axial bearing stator includingmultiple stator poles each including a first coil portion and a secondcoil portion; winding the first coil portion in a first direction; andwinding the second coil portion in a second direction opposite the firstdirection.
 51. A method for magnetically supporting a pump rotor in ahousing for rotation about an axis, the method comprising the steps of:providing a magnetic first radial bearing for exerting a force on therotor in a first direction along the axis; providing a magnetic secondradial bearing for exerting a force on the rotor in a second directionalong the axis opposite the first direction; and adjusting the axialpositions of the first and second radial bearings to independentlyadjust the net axial force exerted on the rotor by the first and secondradial bearings and the radial stiffness of the first and second radialbearings.
 52. The method recited in claim 51, further comprising thesteps of adjusting one of the first and second radial bearings an axialdistance to increase its axial pull on the rotor and adjusting the otherof the first and second magnetic rings the same axial distance todecrease its axial pull on the motor to adjust the net axial forceexerted on the rotor by the first and second radial bearings independentof the radial stiffness of the first and second radial bearings.
 53. Themethod recited in claim 51, further comprising the steps of adjustingthe first and second radial bearings an axial distance toward the rotorto increase the radial stiffness of the first and second radial bearingsindependent of the net axial force exerted on the rotor by the first andsecond radial bearings.
 54. The method recited in claim 51, furthercomprising the steps of adjusting the first and second radial bearingsan axial distance away from the rotor to decrease the radial stiffnessof the first and second radial bearings independent of the net axialforce exerted on the rotor by the first and second radial bearings.